In uranium enrichment as, for example, taught by U.S. Pat. No. 3,772,519 and U.S. Pat. application Ser. No. 328,954, filed Feb. 2, 1973 and patent application Ser. No. 469,407, filed May 13, 1974, incorporated herein by reference, a vapor of uranium is generated and illuminated with laser radiation tuned to produce isotopically selective photo-excitation of, for example, the U-235 isotope. The excited particles are ionized and separately collected on plates using magnetohydrodynamic acceleration forces on the charged particles.
In such a system, the laser radiation is preferably applied in pulses at a repetition rate which insures that all portions of the following vapor are illuminated with the radiation in order to provide efficient operation. To provide laser radiation of this sort a system of multiple lasers has been suggested as represented in U.S. Pat. application Ser. No. 438,029, filed Jan. 30, 1974, incorporated herein by reference, with plural beams of output radiation combined into a single beam of augmented pulse rate by rotating optics. It may occur that for continuous processing according to such a technique, one or more of the lasers may occasionally be nonoperative for an interval of time for such purposes as maintenance, or it may be desired to operate the enrichment system efficiently with less than the total complement of lasers. Additionally, it may be desirable to make short term adjustments to the enrichment apparatus within the vapor environment. For such occasions, it is desired to be able to rapidly extinguish the generation of vapor for a period without loss of heat from the uranium mass to permit rapid restart of the vapor generation. In the case of missing lasers in the laser system such periodic cessation in the vapor generation would occur periodically at a relatively fast repetition rate for very short intervals while in the case of other partial shut down of the processing the interruption would be somewhat longer. Thus it is desirable to provide a uranium vaporization source capable of rapid shut down and restart in both situations with relatively little vapor waste.